obviously for doing work of a scientific nature is best done in metric. I don't think anyone disagrees with that. But I think some of what pz, (the original biased bigot *grin*), was saying that its sometimes useful for people to know both and that in the UK, Aust and NZ lots of people do know both. I don't agree about the Engineers being able to have a convo in imperial or metric.
Personally, I like the imperial system for some lengths. A foot is a very convienent length when talking about height, short distances ( 3m) and length of materials. I find myself using feet quite often when pointing out an object which is 6 foot off the ground, or 2 feet from the wall, etc. Its just the level of precision you can get for those measures of distance which is alot more convenient than 1.8m, or 70cm or 2.2m. You can describe most distances in multiples of half a foot with enough accuracy to convey meaning. In metres is harder..but that said, once your out past 5-6 metres I think its switches back the other way.
Miles and Kilometres is completely different. Neither of them are more convenient than the other so I use the metric.
I live in Australia and my parents were brought up on imperial and it changed (in 1966) so they got to know that one aswell (they were late teens in 1966).
The other thing that contributes to our familiarity is our standard ruler. I grew up with 30cm/12inch rulers.. I suppose its the same today. But I've always been adept at switching inches to mm and back. So I think its fairly common over here.